To answer your last question, arms do not wear out with normal use with two notable exceptions. Arms without sealed bearings, when used in an environment with airborne pollutants, such as cigarette smoke and excessive dust can have problems. Secondly, incorrect mounting of the cartridge can cause tortional forces on captured bearings that result in Brinelling (flat spotting) of the bearings, which is why I suggest mounting cartridges with the arm off of the turntable.
I would also agree that the turntable is the engine of sound, as it were, but it can't wear a record. A sticking bearing, poorly polished, or misaligned stylus can. Just some food for thought. I won't get into the audiophile side of things.